1. Field of the Invention
The present invention relates to an image forming apparatus capable of detecting the environmental conditions under which the image forming apparatus is placed and the density of images, so as to allow the image forming apparatus to form the images with an appropriate image density.
2. Description of the Related Art
It is well-known in the image forming apparatus, such as an electronic copying machine, that the density of images formed is considerably changed by environmental conditions under which the image forming apparatus is placed, that is, by temperature, humidity and atmospheric pressure around the image forming apparatus. Various kinds of measures have been employed to keep the change of this image density as small as possible. For example, environmental temperature is detected and the output of a transformer which causes an electrification charger to generate a charge is changed responsively to the temperature detected. The amount of charge added to a photosensitive drum is thus controlled and the amount of toner supplied from a developing means to the photosensitive drum is kept certain, so that the density of images can be made stable.
In the case of the conventional image forming apparatus, however, the output of the charge generating transformer is only changed by correlation with the environmental temperature. When the photosensitive drums are different in their characteristics and the amount of corona generated by the charge generating transformer is not kept certain, therefore, the amount of charge on the surface of the photosensitive drum cannot be kept certain, thereby to change the density of images formed.